Today's Video

New filtration material could make petroleum refining cheaper, more efficient

This view of the molecular structure of the MOF shows the triangular channels that run through the material. The walls of these channels trap the lower-octane components of gas while allowing the higher-octane molecules to pass through, potentially providing a more efficient and cost effective way to refine high-octane gasoline. Credit: Science

A newly synthesized material might provide a dramatically improved
method for separating the highest-octane components of gasoline.
Measurements at the National Institute of Standards and Technology
(NIST) have clarified why. The research team, which included scientists
from NIST and several other universities, has published its findings in
the journal Science.

Created in the laboratory of Jeffrey Long, professor of chemistry at
the University of California, Berkeley, the material is a metal-organic
framework, or MOF, which can be imagined as a sponge with microscopic
holes. The innumerable interior walls of the MOF form triangular
channels that selectively trap only the lower-octane components based on
their shape, separating them easily from the higher-octane molecules in
a way that could prove far less expensive than the industry's current
method. The Long laboratory and UC Berkeley have applied for a patent on
the MOF, which is known by its chemical formula, Fe2(bdp)3.High-octane gasolines, the ultra or premium blends at fueling
stations, are more expensive than regular unleaded gasoline due to the
difficulty of separating out the right type of molecules from petroleum.
Petroleum includes several slightly different versions of the same
molecule that have identical molecular formulae but varying shapes --
called isomers. Creating premium fuel requires a refinery to boil the
mixture at precise temperatures to separate the isomers with the most
chemical energy. The trouble is, four of these isomers -- two of which
are high octane, the other two far lower -- have only slightly different
boiling points, making the overall process both challenging and costly.

The new MOF, however, could allow refineries to sidestep this problem
by essentially trapping the lowest-octane isomers while letting the
others pass through. The lowest-octane isomers are more linear and can
nestle closer to the MOF walls, so when a mixture of isomers passes
through the MOF, the less desired isomers stick to its surface --
somewhat akin to the way a wet piece of paper sticks to a wall.Matthew Hudson and his colleagues at the NIST Center for Neutron
Research (NCNR) used neutron powder diffraction, a technique for
determining molecular structure, to explore why the MOF has the right
shape to selectively separate the isomers. Their research was essential
to validate the team's model of how the MOF adsorbs the low-octane
isomers.

"It's easier to separate the isomers with higher octane ratings this
way rather than with the standard method, making it more efficient,"
says Hudson, a postdoctoral fellow at the NCNR. "And based on the lower
temperatures needed, it's also far less energy-intensive, meaning it
should be less expensive." Hudson adds that while industrial scientists
will need to work out how to apply the discovery in refineries, the new
MOF appears to be robust enough in harsh conditions to be used
repeatedly a great many times, potentially reducing the necessary
investment by a petroleum company.